This is how you can get it for this price:
Go to o2 via Quidco
and buy O2 standard Broadband £7.34 for a month (1 year = £88.08)
Quidco will give you £70.00 making the total £18.08
This price is only for o2 customer, but if you dont want to go on O2 for your mobile you can always use a O2 pay as you go sim card and bin it afterwards.